Process of manufacture of alkali-metal sulphides



Patented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

HORACE FREEMAN, OF VANCOUVER, BRITISH COLUMBIA, CANADA, ASSIGNOR 0FONE-HALF TO CANADA CARBIDE COMPANY, LIMITED, OF MONTREAL, CANADA.

PROCESS OF MANUFACTURE OF ALKALI-METAL SULPHIDES.

\ No Drawing.

This invention relates to improvements in the manufacture of sodiumsulphide, and the primary object is to obtain a higher yield of animproved product, and in a less time than has heretofore been the case.

A further object is to overcome the inherent difliculties in dealingwith sodium sulphide arising from its practically infusible nature.

A still further object is to render the electric furnace available forthis manufacture.

At present sodium sulphide is commercially produced by heating to abright red heat in a fuel fired furnace, a mixture of sodium sulphatewith a carbonaceous reducingagent, such as coal or sawdust.

As sodium sulphate is fusible, and sodium sulphide is not fusible attemperatures which are commercially practicable in this art, it is foundthat when the proportion of sulphate predominates, as during the earlierstages of the reduction, the charge remains liquid. When about fifty percent of sulphide is formed, the mass thickens and becomes more solid; asa consequence the necessary contact between the reacting particles isprevented and the reduction is checked.

For this reason, the product of this method of operation seldom containsmore than sixty-five per cent of sodium sulphide and is obtained fromthe furnace in the form of a semi-solid mass, which is practicallyelectrically non-conductive even when hot.

In carrying out this process I have found that the imperfections of thismethod of production, viz, the low grade of the fuel fired furnaceproduct and the long period required for the reaction, are due to the infusibility of sodium sulphide, which also introduces complications inits removal from the furnace.

An object of this invention is to render the furnace charge fusiblethroughout the period of operation and in some instances at a lowertemperature than is generally used for the reduction. The charge beingfluid, the reaction is more complete and the yield of sodium sulphide isgreater also owing to its fluidity, the charge is electricallyconductive enabling use of the electric furnace for heating in allstages, and further enabling the sulphide to be tapped from the furnace.

I have found that sodium sulphide which,

Serial No. 619,030.

in the pure state is infusible, or practically so, forms readily fusiblecompounds when mixed with other sulphides, such as those of potassium,calcium, barium, strontium, copper, zinc, lead, iron and many others.

During the course of a long investigation of the products so obtained, Ihave found that the lowering of the fusing point of sodium sulphide isparticularly great when potassium sulphide is added to it: Thus, amixture in proportion of one mole of sodium sulphide to one mole ofpotassium sulphide melts to a thin mobile liquid at 420 degreescentigrade, while the addition of only ten per cent of potassiumsulphide to sodium sulphide produces a mixture melting at 570 degreescentigrade.

Furthermore, the double sulphides of sodium with lead, with zinc, withiron and With copper are very mobile liquids at tem' peratures muchbelow 700 degrees centigrade. Also the double sulphides of sodium withthe alkaline earth metals fuse readily at relatively low temperatures.

Of the alkaline earth metal sulphides, barium sulphide and calciumsulphide have an additional characteristic in common with the heavymetal sulphides, namely, they are insoluble in concentrated aqueoussolutions of sodium sulphide. In this connection it may be noted thatiron and barium sulphides are to some extent soluble in very dilutesolutions of sodium sulphide.

In carrying out this process for the production of sodium sulphide theabove described properties are made use of in the following manneraccording to the product it is desired to obtain.

If the product required is hydrated sodium sulphide, free from admixturewith other sulphides, the reduction of sodium sulphate is carried outwith a reducing agent, such as coal, in the ordinary manner, but when orbefore the previously mentioned thickening of the reacting mass takesplace, a proportion of an insoluble sulphide is added sufficient to makethe charge liquefy or to keep the same liquid. A very small proportionof the added sulphide will liquefy the charge at a temperature of 1000degrees centigrade, while the addition of a molecular proportion of leadsulphide will cause liquefaction of the sodium sulphide at.550 degreescentigrade, and when a molecular pro'portion of zinc sulphide is used,at 620 degrees centigrade.

The common sulphide ores are used for this purpose or refined orrecovered sulphides may be used as obtained in the later steps of theprocess.

The insoluble sulphide may be added to the charge of sulphate and itsreducing agent prior to feeding them into the furnace, or it may beadded at any subsequent stage in order to bring about the desiredresult, viz, the maintaining of the sodium sulphide in the reactionmixture in a liquid condition so that reduction may proceed tocompletion. As an alternative a metal sulphate may be added which willreduce to a sulphide to fuse with the sodium sulphide. During the periodof reduction the carbon monoxide gas produced, easily and quietlyescapes from the mobile liquid. When the evolution of gas ceases,reduction is complete and the charge may be tapped or poured from thefurnace.

The product of this operation is sodium sulphide in admixture orcombination with an insoluble sulphide. In order to obtain pure sodiumsulphide from this material, it is necessary to lixiviate the mass withhot water. The sodium sulphide is readily dis solved in the water butthe other metal sulphide remains undissolved in the form of an extremelyfine suspension, which, however, quickly settles on account of its highspecific gravity. The clear solution'of sodium sulphide is thereforeeasily separated and allowed to crystallize; the product ofcrystallization being sodium sulphide free from other sulphides. 1

It is obvious that the fine sludge of th added metal sulphide resultingfrom this operation is available after drying for re-use in the processof reduction.

If the sulphide product desired is that known as fused sodium sulphideand is to be used without further refinement by crystallization, thepresence of an insoluble metal sulphide wouldrbe objectionable. Thepresence of potassium sulphide or a soluble alkaline earth metalsulphide is ordinarily not objectionable inasmuch as these sulphideswill erform the same function as sodium sulphide in many of its variousapplications in the arts.

As previously stated, potassium sulphide is particularly effective inrendering sodium sulphide fusible in the process of reduction. Less thanten per cent of the potassium sulphide is required and in most casesless than ve per cent of the weight of sodium sulphide is a practicablepro ortion to use, al-

' though I do not desire to e confined to any particular proportion.

My process for producing the fused alkali metal sulphide consists inheating a mixture of sodium sulphate with the desired proportion ofpotassium sulphate and a carbonaceous reducing agent. Potassium sulphideis formed coincidentally with sodium sulphide and the charge remainsliquid while the reduction is carried to completion. As an alternative Imay add previously prepared potassium sulphide to the sodium sulphatecharge undergoing reduction. The result is the same, i. e., theliquefaction of the charge.

The process may be operated similarly using alkaline earth metalsulphides admixed with the sodium sulphate.

The product can then be tapped or run from the furnace direct intocontainers for shipping, it may be cooled in moulds, or it may bequickly cooled on a rotating water- .cooled drum and produced in theform of flakes as is now done with caustic soda and with cyanid.

\Vith the process here described the time required for reduction is muchshortened and a smaller amount of the reducing agent is used than in theprocess heretofore practised. The reduction is carried much farther thanin the usual process, owing to the mobility of the charge in the furnaceand the intimate contact of particles thereby provided.

I do not desire to be confined to any particular form of furnace incarrying out this process, but I prefer and have used an electricfurnace for the purpose, utilizing the charge itself as the resistor.The electric furnace is preferred as it is more economical and avoidsoxidation of the sulphide product which is apt to take place in a fuelfired furnace. My process for the first time makes the electric furnaceavailable for this manufacture, allowing of the tapping of the liquidproduct and dispensing with the use of moving devices for stirring thecharge.

In carrying out any of the variations of this process I may either addthe desired sulphide or sulphides to the charge, or I may, as described,add the corresponding sulphate or sulphates or any other salts whichwill be reduced to sulphides coincident with the reduction of sodiumsulphate. The roduct of the process here described contains lar erpercentages of available sulphide than 1s at all possible by the methodnow commonly used.

Having now particularly described my invention, I hereby declare thatwhat I claim as new and desire to be protected in by Letters'Patent, is:

1. A process of producing a sodium sulphide product of over 60% sodiumsulphide content which consists in fusing sodium sulphate inpresence ofa carbonaceous reducmolten condition until after substantially completereduction of the sodium sulphate is effected.

2. The process ofproducing sodium sulphide which consists in fusingsodium sul phate with a carbonaceous reducing agent llil the presence ofanother alkali metal sulp ide.

3. The process ofproducing sodium sulphide which consists in fusingsodium sulphate with a carbonaceous reducin agent in the presence ofpotassium sulphi e.

4. The process of producing a sodium sulphide product of over sodiumsulphide content which consists in fusing sodium sulphate in presence ofa carbonaceous reducing agent and another sulphate, such as will bereduced to yield a sulphide during the reduction of the sodium sulphate,and heating the reaction to maintain the mixed sulphides in a fluidcondition until after reduction of the sulphates is substantiallycomplete.

5. The process of producing a sodium sulphide compound, which consistsin heating a mixture of sodium sulphate and potassium sulphate witha'reducing agent at a temperature sufficient to maintain the reactionproduct in a molten condition.

6. The product which comprises sodium sulphide fused and associated witha sulphide of another alkali metal.

7 The product which includes sodium sulphide in amount upwards of 60%.of the whole and another metal sulphide, the said product being capableof liquefaction at temperatures a little over 1000 C.

8. The process of making sodium sulphide which comprises fusing togethersodium sulphate equivalent to more than 60% sodium sulphide content ofthe final product and the sulphate of another metal in presence of acarbonaceous reducing agent, and maintaining the sulphide content of themass molten until evolution of gas ceases.

9. The process of making sodium sulphide which comprises reducingtogether sodium sulphate equivalent to more than 60% sodium sulphidecontent of the final product and the sulphate of another metal byheating the same in presence of a carbonaceous reducing agent andmaintaining the sulphide content of the reacting mass constantly in amolten condition.

10. In the manufacture of sodium sulphide by reduction of sodiumsulphate with a carbonaceous reducing agent, the step of maintaining theformed sodium sulphide molten until substantially all the sodiumsulphate has been reduced, which comprises carrying out the reduction inpresence of less than 10% of the sulphide of another metal.

11. In the manufacture of sodium sulphide by reduction of sodiumsulphate with maintainin a carbonaceous reducing agent, the step of theformed sodium sulphide molten unt1l substantially all of the sodiumsulphate has been reduced, which comprises simultaneously reducing thesulphate of another metal in amount less than 10% of the sodium sulphateand retaining the formed sulphide in the reaction in presence of thesodium sulphide undergoing reduction.

12. In the manufacture of sodium sulphide by reduction of sodiumsulphate with a carbonaceous reducing agent, the step of lowering thefusion temperature of the mixed sulphate and sulphide whencontaining'over 60% sulphide and maintaining the same molten at atemperature under 1500 C., which comprises carrying out the reduction inpresence of the sulphide of another metal.

13. The process of producing sodium sulphide which comprises meltingsodium sulphate with less than 10% of a soluble sulphide of anothermetal in presence of a carbonaceous reducing agent.

14. A process of making sodium sulphide by reduction of sodium sulphatewith a carbonaceous reducing agent, which comprises fusing the sulphatein presence of the reducing agent and when the charge commences tothicken fluxing the same with the sulphide of another metal in amountsuflicient to flux the formed sodium sulphide and maintain the samefreely fluid until after substantially complete reduction of the sodiumsulphate is effected.

15. A process of making sodium sulphide by reduction of sodium sulphatewith'a carbonaceous reducing agent, which comprises fusing the sulphatein presence of the reducing agent and when the charge commences tothicken fiuxing the same with the sulphide of another metal in amountsufficient to flux the formed sodium sulphide and maintain the samefreely fluid at a temperature over 1000 C. until after substantiallycomplete reduction of the sodium sulphate is effected.

16. A process of making sodium sulphide which comprises heating sodiumsulphate with a reducing agent to a temperature over 1000 C. in presenceof less than 5% of the sulphide of another metal, whereby the sodiumsulphide. is maintained in molten condition until after substantiallycomplete reduction of the sodium sulphate is effected.

17. A process of making sodium sulphide which comprises heating sodiumsulphate with a reducing agent to a temperature over 1000 C. in presenceof less than 5%. of potassium sulphide, whereby the sodium 125 sulphideis maintained in molten condition until after substantially completereduction of the sodium sulphate is efiected.

18. A process of making a fused sodium sulphide product of over 80%sodium sulphide content, which comprises fusing sodium sulphate with thesulphate or sul- Iphide of another metal in presence of a car- 'onaceousreducing agent.

19. A process of making a sodium sulphide product with substantially nosodium carbonate content, which comprises heating sodium sulphate withthe sulphate of an other metal in presence of a carbonaceous reducingagent at a temperature over 1000 C.

20. A process of making'a sodium sul phide product with substantially noSodium carbonate content, which comprises heating sodium sulphate withthe sulphide of another metal in presence of a carbonaceous reducingagent at a temperature of approximately 1000 C.

21. A process of producing a sodium sulphide product of over 60% sodiumsulphide content, which consists in fusing sodium sulphate in presenceof a carbonaceous re-.

ducing agent and along with the sulphides of any other metals serving toflux the formed sodium sulphide and maintain the same in moltencondition until after substantially complete reduction of the sodiumsulphate is effected.

In testimony whereof I affix my signature.

HORACE FREEMAN.

